The present invention relates to a recording method and a recording apparatus whereby digital data is recorded onto a disc as run-length limited code by modulating digital data used for modulating marks or spaces on the disc and, at the same time, the recorded digital data is encrypted by using key data which is also recorded onto the same disc by variation of the shape of marks or spaces with timing having no effect on the edges of the marks or the spaces. In addition, the present invention also relates to a playback method and a playback apparatus for reproducing the digital data and the key data recorded on the disc by the recording method and/or the recording apparatus from the disc with the key data used for decrypting the encrypted digital data.
In the commonly known related art compact disc, after completing data processing, audio data is subjected to EFM (Eight-to-Fourteen Modulation) to form a series of pits with a period in the range of 3T to 11T where the symbol T is a predetermined basic period. In this way, audio data or other information is recorded in the compact disc.
The compact disc player for playing back a signal from this compact disc radiates a laser beam to the disc and receives a light reflected by the compact disc. The compact disc player then obtains a playback signal having a level varying with the quantity of the received light and compares the playback signal with a predetermined slice level in order to convert the playback signal into a binary signal in a binary conversion process. A PLL circuit is driven to extract a playback clock signal from the binary signal. The extracted playback clock signal is in turn used for sequentially latching the binary signal to generate playback data with a period varying in the range of 3T to 11T corresponding to a series of pits formed on the compact disk.
The compact disc player then decodes the playback data generated in the way described above by carrying out data processing as a counterpart of the data processing performed in the recording operation. As a result, audio data or other information recorded on the compact disc is played back.
In order to effectively avoid an illegal copy in a transfer system for transferring audio data through such an optical-information recording medium, there have been proposed copy preventing systems like those shown in FIGS. 1 or 2.
An encoder 3 employed in a disc producing apparatus 2 in the copy preventing system 1 shown in FIG. 1 carries out scramble processing on data D1 to be recorded on an optical disc 5 by using a master key KM and then records the data completing the scramble processing on the optical disc 5. On the other hand, a decoder 7 employed in a playback apparatus 6 carries out descramble processing on playback data reproduced from the optical disc 5 typically by using the shared master key as the disc producing apparatus 2. Then, a decoder 8 complying with MPEG (Moving Picture Expert Group) specifications processes data obtained as a result of the descramble processing. Thus, in the copy preventing system 1, the encoder 3 scrambles the data D1 by using the predetermined master key KM shared with the playback apparatus 6 in order to prevent an illegal copy.
In the copy preventing system 10 shown in FIG. 2, on the other hand, data D1 is scrambled by using a master key KM, a disc key DK unique to an optical disc 11 and a title key KT unique to a work recorded on the optical disc 11. To put it in detail, an encoder 13 employed in a disc producing apparatus 12 carries out scramble processing on the disc key DK by using the master key KM and records the disc key DK completing the scramble processing on the optical disc 11. Then, an encoder 14 employed in the disc producing apparatus 12 carries out scramble processing on the title key KT by using the disc key DK completing the scramble processing and records the title key KT completing the scramble processing on the. optical disc 11.
Subsequently, an encoder 15 employed in the disc producing apparatus 12 carries out scramble processing on the data D1 to be recorded by using the title key KT completing the scramble processing and records the data D1 completing the scramble processing on the optical disc 11. The disc producing apparatus 12 carries out multiple scramble processing on the data D1 with the master key KM used as a reference and records the data D1 completing the multiple scramble processing on the optical disc 11.
A decoder 17 employed in a playback apparatus 16 carries out descramble processing on the disc key DK completing the scramble processing by using the master key KM to decode the disc key DK. A decoder 18 employed in a playback apparatus 16 then carries out descramble processing on the title key KT completing the scramble processing, by using the disc key DK to decode the title key KT. Subsequently, a decoder 19 employed in a playback apparatus 16 carries out descramble processing on the data D1 completing the scramble processing by using the disk key DK.
The copy preventing system 10 adds the functional positions of the disc producer and the author of the work to the scramble and descramble processes, avoiding an illegal copy.
By the way, there are two types of illegal copy. An illegal copy of the first type is produced by using a result of decoding a master key. As a result, an illegal user is capable of reproducing a signal from the illegal copy by using a playback apparatus even if the illegal copy is produced as a result of piracy. An illegal copy of the second type is produced by physically copying a pit form created on a legal optical disc.
In a copy preventing system based on a master key, the problem of an illegal copy of the first type can be solved by making it difficult to decode the master key. This solution has a shortcoming, however, that once the master key has been decoded, it is no longer possible to avoid piracy of discs whatsoever. In addition, this solution is not applicable to piracy to produce an illegal copy of the second type.
It is thus an object of the present invention addressing the problems described above to provide a recording apparatus, a recording medium, a playback apparatus, a recording method and a playback method which are capable of effectively preventing illegal copies.
According to an aspect of the present invention, there is provided a recording apparatus for successively recording digital data as alternating marks and spaces on a disc by modulation of said marks or said spaces in a run-length direction thereof in accordance with said data, said recording apparatus comprising: a key data generating means for generating key data; an encryption means for encrypting said digital data on the basis of said key data generated by said key data generating means; a key data modulation means for modulating said marks or said spaces in a width direction thereof in accordance with said key data generated by said key data generating means; and a recording means for recording said key data used in modulation of said marks or said spaces carried out by said key data modulation means in a width direction thereof and digital data encrypted by said encryption means.
According to another aspect of the present invention, there is provided a disc-shaped recording medium for storing digital information encrypted by using predetermined key data on recording tracks by modulation of a series of alternating marks and spaces on each of said recording tracks, said disc-shape recording medium comprising: a program area having a plurality of said recording tracks wherein said encrypted digital information is recorded by modulation of said marks or said spaces in a run-length direction thereof; and a lead-in area for recording said key data by modulation of said marks or said spaces in a width direction thereof.
According to still another aspect of the present invention, there is provided a playback apparatus for reproducing key data and digital data encrypted by using said key data from a disc-shaped recording medium wherein: said digital data is recorded by modulation of marks or spaces in a run-length direction thereof in a program area of said disc-shaped recording medium; and said key data for decrypting digital data is recorded by modulation of marks or spaces in a width direction thereof in a lead-in area of said disc-shaped recording medium, said playback apparatus comprising: a playback means for reproducing information from said lead-in area; a demodulation means for demodulating said information reproduced by said playback means from said lead-in area on the basis of variations in mark or space in width direction to decrypt said key data; and a decryption means for decrypting said digital main data recorded in said program area by using said key data resulting from demodulation of said information by said demodulation means.
According to a further aspect of the present invention, there is provided a recording method for recording digital main data as alternating marks and spaces on a disc by modulation of said marks or said spaces in a run-length direction thereof in accordance with said data, said recording method comprising the steps of: generating key data; encrypting said digital main data on the basis of said key data; and recording said key data by modulation of said marks or said spaces in a width direction thereof in accordance with said key data and recording digital data encrypted on the basis of said key data by modulation of said marks or said spaces in a run-length direction thereof in accordance with said digital main data.
According to a still further aspect of the present invention, there is provided a playback method for reproducing key data and digital main data encrypted by using said key data from a disc-shaped recording medium wherein: said digital main data is recorded by modulation of marks or spaces in a run-length direction thereof in a program area of said disc-shaped recording medium; and said key data is recorded by modulation of marks or spaces in a width direction thereof in a lead-in area of said disc-shaped recording medium, said playback method comprising the steps of: reproducing information from said lead-in area; demodulating said information reproduced from said lead-in area on the basis of variations in mark or space in a width direction to produce said key data; and decrypting said digital main data recorded in said program area by using said key data resulting from demodulation of said information.